Instrumentation & Measurement Magazine 23-3 - 10

Basic Metrology for 2020
Richard Davis and Stephan Schlamminger

019 was a big year for metrology. The international
system of units was revised on World Metrology Day,
May 20th, that year [1]. What will 2020 bring? In this
article we discuss five promising advances that we have on a
watchlist for 2020. First, we describe the measurement of volume and gas pressure using electromagnetic waves. These
measurements rely on the fixed value of the speed of light in
vacuum c0. We then pivot to the Planck constant h. SI traceable
measurements of mass and force can be obtained from h. Interesting developments are coming in mass metrology since
the definition changed from the mass of the international prototype of the kilogram to the value of the Planck constant.
Adding the elementary charge e to h gives access to resistance
and impedance measurements via the quantum Hall effect.
This has been a very interesting field for some time, since the
discovery of graphene in 2004. The last section explains how
the noise across a resistor can be used to measure thermodynamic temperature. As will be shown, the temperature can be
linked to the quotient of the Boltzmann constant kB and the
Planck constant.
While it is difficult to compete with the excitement in metrology of the last year, we are convinced that fun and exciting
developments are in store for basic metrology in 2020.

standpoint of metrology, the goal of the work described below
is to reduce the number of steps in the present calibration chain
by developing a gas-flow standard that operates at higher
pressures and flow rates [3].
The main component of the prototype apparatus is referred
to informally by the NIST researchers as the Big Blue Ball (BBB).
Shown in Fig. 1, it has a nominal inner volume of 1.8 m3 (1800 liters) and can be pressurized to 7 MPa (70 atmospheres) for use

Weighing a Gas with Microwave and
Acoustic Resonances
Prior to the revision of the SI in May 2019, achieving better
measurements of the Boltzmann constant kB using different
methods was a priority. The method that achieved the lowest
uncertainty relied on measuring acoustic and microwave resonances in a spherical cavity.
Today, the same equations that described those measurements can be rearranged to measure other quantities in novel
ways. The example shown here is the development of a new
apparatus which could eventually replace the present primary standard for gas flow [2] used by the National Institute
for Standards and Technology (NIST). Flow measurements
are economically important (the value of natural gas metered
in US pipelines was about $90 billion in 2016 [3]). From the
10

Fig. 1. The Big Blue Ball. It is made of carbon steel, has an inner volume of
about 1800 liters, and weighs more than 1000 kg. (photo credit: NIST's Fluid
Metrology Group).

IEEE Instrumentation & Measurement Magazine
1094-6969/20/$25.00©2020IEEE

May 2020

Instrumentation & Measurement Magazine 23-3

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